Along with the development of software and hardware techniques, commercial and household 3D display apparatuses become matured and 3D images have also become a great development trend in multimedia. Current 3D image display techniques are in general categorized into active and passive types, which shall be described below.
The active 3D image display technique alternately presents left-eye and right-eye images on a single monitor. Dedicated glasses worn by a viewer shield a right eye of the viewer when a left-eye image is presented and shield a left eye of the viewer when a right-eye image is presented. A visual system of the viewer automatically combines images successively received by the both eyes to 3D images. Due to vision persistence, the brief shielding by the 3D glasses against the presented images remains unnoticed by the viewer as long as a switching frequency of the left-eye and right-eye images is fast enough. However, the active technique suffers from a drawback that, a wireless communication mechanism is necessarily provided at both terminals in order to achieve synchronous switching of the images on the display apparatus and the switching of the 3D glasses. Thus, the 3D glasses not only cost more but also are bulkier. In addition, flickers in visual effects are incurred when image data lower than 60 Hz is presented to the human eyes, and further lead to discomfort of the eyes. Therefore, since the active 3D image display technique alternately presents left-eye and right-eye images on a single monitor, a display system of the active 3D image display technique needs to support a display frequency double to that of a common display system to render an equivalent display frequency with respect to the human eyes. In other words, the active display technique is only suitable for display systems supporting up to a frame rate of 120 Hz, and is hence not widely adopted.
On the other hand, the passive 3D image display technique simultaneously presents left-eye and right-eye images in a single image frame. As shown in FIG. 1, odd-row pixels R1, R2, R3 . . . correspond to the right-eye image, and even-row pixels L1, L2, L3 . . . correspond to the left-eye image. Take a display with a vertical resolution of 1080 pixels as an example, the image frame comprises two images—540 rows of right-eye image data and 540 rows of left-eye data, which are horizontally staggered.
A passive 3D image display comprises an exteriorly adhered polarizing film. For example, a polarization angle corresponding to the odd-row pixels R1, R2, R3 . . . may be designed as 45 degrees, and polarization angle corresponding to the even-row pixels L1, L2, L3 may be designed as 135 degrees. Thus, a left lens and a right lens of the glasses worn by the viewer only allow the passing of light beams with a polarization angle of respectively 45 degrees and 135 degrees, so that different images are respectively received by the left and right eyes. Similarly, the viewer automatically combines images respectively received by the both eyes simultaneously through human visual characteristics to form a corresponding 3D image.
The polarizing film is an inexpensive material, and an overall cost of the passive 3D display system is relatively low. In addition, glasses for the passive 3D display system are also simpler and compact than those for the active system. Consequently, the passive 3D image display system has a greater market share.
In continuation of the above discussion, the image frame shown in FIG. 1 is formed by the alternately arranged left-eye and right-eye images, in a way that the horizontal resolution for respectively presenting the left-eye image data and the right-eye image data is only 540 pixels. However, the horizontal resolution of original left-eye and right-eye image data initially inputted is both 1080 pixels. To provide the left-eye and right-eye image data with a 540-pixel horizontal resolution, the original left-eye and right-eye images need to first undergo appropriate calculations and merging. One of the most common calculation and merging approach is to average two neighboring rows of pixels of the original right-eye (left-eye) image to generate a row of pixels to be displayed. For example, an average of the uppermost first and second rows of pixels in the original right-eye image is calculated to generate the first-row pixel R1 in FIG. 1. Similarly, the uppermost third and fourth rows of pixels in the original right-eye image are calculated to generate the third-row pixel R2 in FIG. 1. Such approach however also suffers from a drawback that, the horizontal resolution of the images perceived by the left and right eyes of the viewer is only 540 pixels even though the horizontal resolution of the display is 1080, meaning that a data amount of the original image is halved. As a result, the image may appear as having insufficient luminance, details and clearness to the viewer.
To solve the above issue of insufficient details provided by the passive 3D image display system, a frame-rate doubling conversion associated with the prior art is proposed. For example, 60 Hz is up-converted to 120 Hz. In other words, apart from distinguishing the left-eye and right-eye images with a spatial separation technique, the above prior art further adopts a temporal separation technique to enhance an image resolution. In the above prior art, original left-eye images and right-eye images are respectively divided into two groups. As shown in FIG. 2A, at 1/120 second, an image displayed on the monitor comprises odd-row data (RO1, RO3, RO5 . . . ) of an original right-eye image and odd-row data (LO1, LO3, LO5 . . . ) of a corresponding original left-eye image. Also, as shown in FIG. 2B, at 2/120 second, an image displayed on the monitor comprises even-row data (RO2, RO4, RO6 . . . ) of the original right-eye image and even-row data (LO2, LO4, LO6 . . . ) of the original left-eye image.
As shown in FIG. 2A and FIG. 2B, all data of the original right-eye and left-eye images are presented to the image frame. Within 1/60 second, image data entering the visual system of a viewer is thus more than that shown in FIG. 1, so that the viewer truly feels the details of the image are enhanced. However, due to the temporal separation, although the frame rate of the images displayed on the display system is in fact doubled to 120 Hz, a frame rate perceived to the human eyes maintains 60 Hz. Therefore, the conventional technique shown in FIG. 2A and FIG. 2B is not quite prevalent since it is only suitable for display systems capable of doubling the frame rate to 120 Hz.